The error message is :

 Error while loading item prototype "rf-solid-light-oil" (item): Value must be a string in property tree at ROOT.item.rf-solid-light-oil.icons[1].icon
Modifications: Reverse Factory

I don't have any more information. I have tried to find the error myself. It is probably due to the fact that nested icons are not handled correctly. My suggested change is:

    if fluid.icons then
        for _, added_icon in pairs (fluid.icons) do
            -- This line may not work, icon_size is assumed vanilla default, scale is weird
            <b>table.insert(new_item.icons,{icon=added_icon.icon,icon_size=added_icon.iconSize,scale=0.45, tint = added_icon.tint})</b>
        end
    elseif fluid.icon then
        table.insert(new_item.icons,{icon=fluid.icon,icon_size=iconSize,scale=0.5})
    end

This occurs in two places in func.lua. The comment already indicates that you knew that something was wrong (-; Unfortunately, I can't offer you anything with simple means where you can easily reproduce the error.

Yup, at the time of the initial update regarding fluids, I only had the base game to work with, which doesn't use multi-layer icons, so I couldn't quite test how functionality might work and just made a best guess. I didn't think any mods would require this functionality for fluids, which makes me wonder which mod could be causing this.

If you load up the game without Reverse Factory, you should be able to look at Light Oil in the Factoripedia, and see which mods are affecting it. One of them must be changing it, because this error doesn't happen in vanilla

It came from a very old mod called palette cleanser.
This mod has not been maintained by the inventor for versions. But I need it and have always brought it up to date myself in a makeshift manner. But I never had the time to fork it. That's why I said it's not easy to reproduce.
The feature is probably not needed very often.
If you want, you can test the fix with my variant of this mod here (https://github.com/hahoyer/factorio-mod-palettecleanser). Then you'll be prepared if it occurs again.

Btw. I have already tried the patch in a private version of your mod. I use a few mods and have already got as far as Vulcanus.

Here is my modlist:
4.198 Checksum for core: 3504056361
4.198 Checksum of base: 48730768
4.198 Checksum of comfortable-loader: 2486588771
4.198 Checksum of ixuAutoSave: 623976035
4.198 Checksum of squeak-through-2: 1101572755
4.198 Checksum of AfraidOfTheDark: 2425600053
4.198 Checksum of AutoDeconstruct: 3603960023
4.198 Checksum of Automatic_Train_Painter: 2774037699
4.198 Checksum of creative-mod: 1442951274
4.198 Checksum of elevated-rails: 971617432
4.198 Checksum of flib: 2235140407
4.198 Checksum of HandyHands: 3023818343
4.198 Checksum of ixuClock: 0
4.198 Checksum of kry_stdlib: 0
4.198 Checksum of loaders-utils: 608236998
4.198 Checksum of nixie-tubes: 1894147257
4.198 Checksum of palettecleanser: 2820979543
4.198 Checksum of qol_research: 3109955847
4.198 Checksum of quality: 3898255384
4.198 Checksum of RadarMarker: 159568847
4.198 Checksum of ShorterGermanKeyNames: 0
4.198 Checksum of show-max-underground-distance: 1201560390
4.198 Checksum of showTileGridLite: 1665395947
4.198 Checksum of BottleneckLite: 310795685
4.198 Checksum of ixuGeheimlabor: 763912616
4.198 Checksum of silent-filter-combinator: 3815114475
4.198 Checksum of space-age: 1545753807
4.198 Checksum of WideChests: 4097505498
4.198 Checksum of reverse-factory: 1576194881

I'm not sure if the version of your mod was working correctly, or if something in my testing folder was affecting it, but I was at least able to fix the load error by deepcopying each added_icon in the fluid.icons table, and then modifying the scale to what should be the correct dimensions.

At least, I believe it should be copying and rescaling pre-existing icons properly, but something about light oil was messed up for any recipe that was using that icon, and it came out too small when I checked it (though I don't believe any of that will be noticeable in-game, since I override all of those icons with my premade customized ones instead, unless you prevent the overrideFluidIcons and overrideFluidRecipe functions from running)

Should be fixed in v9.0.11

Oh, I'm very sure that my version of the mod is faulty. As I said, I've only fixed it in a makeshift manner. That's why I don't want to publish it. ((-:

Btw. Thank you for recycling the pistol now.